Hydraulic brake safety device



Oct. 11, 1949.

Filed July 27, 1948 Fig. I.

E. E. MAPES ETAL 2,484,177

HYDRAULIC BRAKE SAFETY DEVICE 3 Sheet-Sheet 1 Elswprrh E. Mapes Russell E. Cox

INVENTORS Oct. 11, 1949. E. E. MAPES ETAL 2,484,177

HYDRAULIC BRAKE SAFETY DEVICE Filed July 27, 1948 s. Sheets-Sheet 2 Elsworrh E. Mapes Russell E. Cox

, JNVENTORS E. E. MAPES ET AL HYDRAULIC BRAKE SAFETY DEVICE Oct. 11, 1949.

3 Sheets-Sheet 3 Filed July 27, 1948 Elsworrh E. Mapes Russell E. Cox

12W ENTORS Attamqvs Patented Oct. 11, 1949 HYDRAULIC BRAKE SAFETY DEVICE- Elsworth'E. Mapes and Russell E. Cox, Mena, Ark.

Application July 27, 1948, Serial No. 40,804 a:

8 Claims.

This invention comprises novel and useful improvements in a hydraulic brake safety device and more specifically pertains to a safety device incorporated in a slave cylinder assembly interposed between the master cylinders and the wheel cylinders of a hydraulic brake system for vehicles and the like.

vThe principal object of this invention is to provide a safety device which may be applied between the pedal operated master cylinder and the individual wheel brake cylinders for improving the operation of the latter, for preventing a leak in a wheel cylinder or its operating brake line for rendering the entering hydraulic brake system inoperative, and for indicating the presence of abnormal travel of the slave cylinder pistons occasioned by a shortage of brake fluid in one of the brake cylinder operating lines or by the need for adjusting the brake shoes.

An important feature of the invention resides in the provision of a slave cylinder assembly which may be readily interposed between a master brake pedal operated cylinder and the individual wheel brake cylinders, whereby a leak in one of the wheel cylinders or its hydraulic brake line will not bleed the entire system of hydraulic fluid or render the same inoperative.

A further feature of the invention resides in the provision of a slave cylinder assembly as set forth in the preceding paragraph, wherein a plurality of slave cylinders are provided, each operatively connected by a single hydraulic line with the foot pedal operated master cylinder, each of the slave cylinders being operatively connected to one or more of the wheel cylinder hydraulic lines for actuation of the wheel cylinders in response to operation of the master cylinder.

Yet another important feature of the invention resides in the provision of a slave cylinder assembl as set forth in the foregoing features 49 wherein a plurality of parallel cylinders are provided having slave pistons reciprocable therein, and wherein there are provided detachable head plates at opposite ends of the cylinder assembly for obtaining access to the actuating and actuated chambers of the slave pistons.

Yet another feature of the invention resides in the provision of a slave cylinder assembly as set forth in the foregoing features wherein the common head plate for the pressure or actuating chambers of the slave pistons is provided with a single closure plug for filling the same, which closure plug extends into a portion of each of the slave cylinders, and is provided with switch means for energizing a signaling circuit'together with stop means for prevent'i mean-s by undue travel-of the slave pistons.

A still further important-feature of the invention resides in the provision :of a removable plug as set forth in the foregoing feature, wherein that portion of the plug extending into each of the slave cylinders carries a first switch means and a second switch means, together with a movable actuating member for successively energizing the two switch means, the actuating member being engageable by and operable by its slave piston when the latter has traveled a predetermined distance in the cylinder, for successively indicating a preliminary and a final warning or signal.

Yet another importantfeature of the invention resides in the provision of a removable plug as set forth in the foregoing feature, wherein that portion of the plug extending into each slave cylinder is provided with an inwardly extending stop, engageable with a surface upon the slave piston for limiting inward movement thereof and protecting the switch actuating member from damage thereby, and wherein the actuating memberis carried by the stop.

A still further important feature of the invention resides in the provision of a fastening means for engaging and retaining the actuating member when the latter has been moved into position with the final warning signal switch.

A still further and additional feature of the invention resides in the provision of a removable closure plug as set forth in the foregoing features, wherein the entire safety switch and stop mechanism may be removed as a unit from each of the slave cylinders for inspection, servicing or repairs as desired, and wherein such movement is necessary in order to release the fastening means from holding the actuating member in its final warning locked position.

And a final important feature of the invention to be specifically numerated herein resides in the provision of aslave cylinder assembly as set forth in the preceding features, which may be readily app-lied to existing hydraulic brake systems or may beconveniently incorporated in such systems during the manufacture of the same, and in which the principles of the invention are equally adaptable to installations wherein one or more wheel cylinders may be controlled by one of the slave cylinders.

These, together with various ancillary features and objects of the invention which will later become apparent as the following description proceeds, are attained by this device, preferred embodiments of which have been illustrated by way of example only in the accompanying drawings, wherein:

Figure 1 is a top plan View showing diagrammatically the manner in which the slave cylinder assembly may be applied and connected with a conventional form of hydraulic brake system and operatively connected to the pedal operated master cylinder and the individual wheel brake cylinof the slave cylinder assembly;

Figure 4 is an end elevational view of one of thefswiteh elements;

' Figure 5 is a longitudinal sectional view through the'insulating core and.stationaryterminals of one of the switch elements; 5

Figure 6 is a wiring diagram-of a" suitable electrical circuit which may be applied in either of,

the embodiments OfFigures-Z and 7;

Figure 7 is a View similar to Figure 2 but showing a modified embodiment of the slave cylinder assembly;

Figure 8 is a vertical transverse, sectional view taken substantially on-the plane-of the section line 88 of Figurel; and

Figure 9 is a vertical vtransversesectional view taken upon the plane of: thexsecti'on line 9-9 of Figure 7.

Referring now more specifically to the accompanying-v drawings, wherein like numerals desi nate similar parts throughout the various views, attention is directed firstxto the embodiment set forth in Figures 1-6, wherein in -Figure 1 there is disclosed the chassis or runninggear framework of an automotive vehicleof anysuitable type to which the principlesgof this invention may be applied, this framework being' denoted by the numeral H3. Mounted upon the framework many desired m'anner is. a .master-cylinder l2 connected with a foot pedal l4 for-operation thereby, whereby the individual=wheel-or cylinder brakes controlling the brake mechanisms for each wheel,

indicated generally by the numerallt, maybe operated. The wheel brake assemblies for the front wheels of the-vehicleare provided with hydraulic brake operating lines ,l8,.while the rear wheel brake assemblies are provided with similar brake operating lines 2ll,,all in accordance with conventional design.

Heretofore, in the conventionalhydraulic brake operating mechanism fora vehicle the master cylinder I2 is directlyconnecte'd withthe lines l8 and 20, whereby all of the wheelcylinders are simultaneously energized by a single application from the master cylindeiv 12 as the foot brake I4 is operated. Howeven in accordance with the principles of this invention,;the discharge line 22 connecting the master cylinder [2- with the individual wheel cylinder lines hasinterposed-therein and connected thereto a; slave-cylinder assembly 24 to be hereinafter-described, this cylinder separately controlling and energizing the hydraulic lines it of'the front brakesand thehydraulic lines-2t of the rear brakes as set-forth hereinafter. e

As will be best seen by reference to Figure 2, the slave assembly 24 preferably includes a casing ZG-ofanysu'itabIe-material,- this casing bein provided with" a pairof substantiallyparallelbores 28 and 30 at one end thereof, these bores extending through one end of the casing 26 and being closed by a removable end cover plate 32 retained as by fastening screws 3d or the like. Slidably received in the bores 28 and 30, are a pair of slave pistons 36 and 31 of similar construction, which in any suitable manner have a fluid-tight fit in the bores 28.

Thus, a packing means 35 of any known construction maybe provided, and the outer ends of the pistons 36 and 31 are preferably provided with identical diametrically reduced axial extensions 39 which are of less diameter than the bores 28' and-36 to provide an annular space therearound, for a purpose to be later set forth.

Aligned with the bores 28 and 3!] are respective bores 38 and 4,0 which as shown may be of a reduced diameter, although if desired these bores may be of greater diameter than the bores 28 and 30. The bores 38 andflfl extend through the other end of the casing 26, and are closed bya removable cover plate 4'2 detachably mounted thereon-as by fasteningscrews 44 or the like. A pair of pistons stand 48 of identical construction are slidably received in. the bores 38- and 40, these pistons being provided with suitable packing means of any known type, and being rigidly connected tothe pistons 36 and 31, as by rigid connecting rods 59 and 52. -As shown in Figure 2, partitions 5d and fifidivide the bores 28 and 38.v

and stand it, respectively, and the piston rods 5% and 52 are slidable through suitable apertures in these partitions. I

The cover plate 42 is provided with suitable removable plugs 58 by'means of which fluid may be supplied to and air or fluid bledfrom the chambers between the-pistons 46 and 48 and the head plate 42, as desired or found to be expedient.

Passages 60 and fiz formed in the head plate 42 freely communicate with the chambers in the cylinders 38 and fill to the right of pistons Mi and t8, and these passages communicate with a com-. mon source of fluid pressure, namely, the pre-- viously mentioned conduit 22 constituting the discharge or delivery conduit from the master cylinder l2. It will thus be seen that upon actuation of the master cylinder by the pedal l4, fluid will'be displaced equally to the two chambers between the pistons .6 and 48 and their head plate 42, to thereby equally apply a force urging these pistons, and consequently the pistons 36 and 31, toward the left of Figure 2.

Suitable compression springs 66 are mounted in the bores 38 and 48 and-are seated between the partitions 5d and 5t and the left ends of the pistons 66 and dB, to thereby yieldingly urge the piston assemblies towards the right or in their outward position in the slave cylinder casing.

As will be more readily apparent from Figures 2 and 3, the head plate 32 is provided with discharge passages 68 and H! which respectively communicate with the pressure chambers formed between the head plate 32 and the left ends of the pistons 36 and 31 in the cylinders 28 and 30, the passages 68 and it being respectively connected to the hydraulic brake lines l8 and 20, whereby the piston 36 will displace fluid and therefore operate the two front brake cylinder assemblies by means of the lines I8, while the piston 3'! will displace fluid in and operate the rear brake cylinders through the lines 29.

This construction has the advantage that if a leak would occur in any of the four hydraulic lines, only one set of two individual wheel cylinders would be rendered inoperative or impaired in its actuation, while the other cylinder would still be maintained filled with fluid and continue in operation. Thus, the effectivenes of the brake system upon a vehicle is greatly enhanced, and the safety of operation of the vehicle is improved.

As will be readily understood, any suitable means not shown may be provided for venting the chambers in the bores 28, 39, 38 and 49 on the adjacent sides of the pistons 36 and 46 and 31 and 48.

It is, however, an essential and basic feature of this invention to provide an indicating means for giving warning when any of the brake lines develop a leak by lacking in fluid, or undue travel occurs in the movement of the slave piston assemblies. It is further desired that this signaling means shall include compactly arranged elements whereby the entire signaling assembly may be removed bodily from the slave cylinder assembly with a minimum of effort, for rapid replacement or servicing or repairs as desired.

Accordingly, in furtherance of this purpose, the closure plate 32 is provided with a substantially axial opening 12, within which is detachably secured a closure plug I4 as by means of fastening screw I6, the inner end of this plug having a shoulder portion seated upon a flange in the aperture 12 as shown. The inner surface of this plug is thus fully exposed to both of the pressure chambers of the cylinders 28 and 39 as will be apparent. It is preferably desired that the end of the closure plug I4 shall be seated against the end of the partition I1 which is an integral part of the slave cylinder assembly casing 26, and is interposed between the two bores 28 and 39. If desired, suitable sealing means, not shown, may be interposed to establish a leakproof joint at this point between the two cylinder pressure chambers.

The inner surfaces of plug I4 are provided with a pair of axially extending bores or recesses 18, in which are removably seated insulating plugs 89 of any suitable dielectric material, these plugs having annular flanges 82 engaging cooperating counterbores at the open extremities of the bores 18, whereby the dielectric plugs may be securely seated in a substantially liquid-tight manner. It is contemplated that the bores I8 shall be so arranged upon the plug 14 as to enable the dielectric plugs to be positioned closely adjacent the partition member 11 between the two pressure chambers of the cylinder bores 28 and 39, for a purpose which will be later apparent.

Extending through each of the insulated plugs 89 is a pair of electrical conductors 84 and 86 to which are attached cables enclosed in housings 88 and 99, one such conduit or housing being provided for each of the cylinders 28 and 39. The ends of the conductors 84 and 86 are headed as at 94 and 92, respectively, to provide electrical contacts on the surface of the plugs 89 which are exposed to the interior of the pressure chambers of the cylinders 28 and 39. Carried by one of the conductors as 84, is a metallic electrically conductive hook fastener 96 for a purpose to be presently set forth.

The plug 14 is provided adjacent each of the insulated plugs 89, with an integral lug or boss 98 which extends inwardly of the cylinder bores 28 and 39, and a flexible metallic movable switch contact I99 of the leaf spring type, is carried by each of the lugs 98 in position for selective and sequential engagement with the headed contacts 92 and 94. The arrangement is such that after 75 stantially inoperable.

fixed contacts 92 and 94, until eventually the end of the movable contact I99 engages the hook fastener 96 carried by the contacting terminal 94, to thereby establish a ground for the electrical conductor in the housings 88 or 99, to which the terminal '84 is connected, thereby energizing a warning signal as set forth hereinafter.

Upon further inward movement of the member 39, which inward movement results in the hooked fastener 96 being positioned in the annular space between the reduced portion 39 and the walls of the cylinder bores 28 and 39, the

spring contact I99 is moved still further inward until the same engages the fixed terminal 92,

thereby energizing the second electric conductor disposed in the housings B8 and 99.

It will be noted that when the pistons 36 and 31 are withdrawn, the flexible spring contacts I99 disengage their fixed contacts, unless there has been sufficient movement to force the end of the flexible contact I99 beneath the hooked fastener 96. When this occurs, however, the flexing of the spring I99 is no longer sufficient to disengage this contact, whereby the circuit controlled thereby will continue to be engaged, until such time as the plug 14 is removed and the resilient contact reset by hand.

For an understanding of the purpose of this electrical contact arrangement, attention is directcd to the wiring diagram of Figure 6, wherein it will be seen that a suitable source of electric current such as the vehicle storage battery I92, is grounded to the frame of the vehicle as at I94, and is provided with a live conduit I96. The latter is then connected to the signal lights I98 and H9 and by means of the leads II2 while leads I I4 continue the circuit through these lights to the switch terminals 92 and 94, respectively, these terminals being engageable by the switch I99, from whence the current is grounded as at 98.

A second pair of lights H6 and H8 are similarly connected as by leads I29 to the live wire I96, while grounds I22 connect those lights to the terminal contacts 92 and 94, which under the control of the spring switch contact I99 are grounded as at 98.

It is contemplated that the first energized contact, namely, the contact 92, will energize warning signal lights I98 and H8 associated with the two slave cylinders 28 and 39, so that as soon as there is a shortage of fluid in the hydraulic system with which the respective pistons 36 and 31 are associated, the corresponding piston will be free to move inwardiy more than its normal operating stroke, in response to operation of the foot pedal I4, so that when sufficient lost motion occurs, for any of a variety of reasons, the portion 39 of the piston will actuate the switch member I99 to energize the corresponding signal light, thus telling the driver of the vehicle at a glance that one set of the brakes of the hydraulic brake system is in dangerous condition. Upon further inward movement beyond the normal travel of the corresponding piston, the latter will not only close the warning signal contacts but will further activate the danger signal contact, this indicating that the piston has moved in its entire possible travel, or substantially so, and that the brakes controlled by that slave piston are sub- This warning signal as seem above mentioned will continue to be energized until; suchtimeasthe plug I4 is removed for. restorationof the terminal contacts to their normala position, whereby a person driving the vehicle will know that the signaling system has been manual-1y: restoredto its normal position, thus indicating that the defective condition has been repaired.

It should be noted that the removable plug I4 provides a convenient and easy means for obtaining access to both of the pressure chambers of the cylinders 28 and 3i), by removing a single closure; plug, wherebyreplenishment of the fluid therein-, -servicing or adjustment of the switches may be readily effected. Further, by this arrangement, a single plug is provided which carries bo th.of the switch members of each cylinder,

and positions them in an operative position for convenient actuation. I

Attention is'now directed to Figures 7-9 disclosing a modified form of the principles of the invention. In this arrangement, the slave cylinder. assembly has been indicated at I24, and as in the previously described device includues a cylinder casing or block I26, which is provided With a pair of parallel cylinders I28 and I33 extending entirely through this block, the openings of the block at the opposite ends being provided with removableclosure plates I32 and 32, detachably secured to the block as by fastening means I34 and I45. Pistons I36 and 531 are respectively slidable in the cylinders I28and I323, these pistons being provided with suitable packing means I39. of. conventional design, and the pistons further having. central, axially extending diametrically reduced hub portions I4 I- is provided with the filler plugs I58, and with passages I60 and IE2 communicating with the fluid chambers between the pistons I36 and I3} and the head I42, these passages being freely connected and communicating with the abovementioned conduit 22 connected with the master brake cylinder I2, :above mentioned- Suitable compression springs I66 are positioned in the cylinders I28, I30 seated at one of their ends against the pistons I35, I37, while their other ends abut the inner surface of the closure plate I 32. These springs, as do the springs 66 in the previously described embodiment,-thus urge the respective piston assemblies toward their right hand or idle position, and thus serve to force-the fluid back into the master cylinder through the conduit 22, by releasing the pressure upon the brake-cylinders of .the Wheel assemblies, .and permit the latter to assume their inoperative positions.

The opposite head or closure plate I32 is provided with passages I68 freely communicating with the interior of the bores. I28 and I30, and which passages are, in turn, connected with the hydraulic brake lines extending to the individual wheel brake assemblies, it being understood that one cylinder I28 will be connected to one set of brakes, either the front or the rear wheels, while the other cylinder I30 will be connected to the other set of wheel brakes.

In this embodiment, the head plate I32 is provided with apertures or bores which are disposed axially of the respective cylinders 528, I36 and insulating or dielectric plugs I 39 are seated in each bore, these plugs having flanged or headed portions I'IIJ seated in corresponding counterbored shoulder recesses in the above-mentioned apertures while the other ends of these insulated plugs are screw-threaded for the reception of The closure plate M2 insulating retaining. glands I 'l2qwhich are, threaded upon the plugs and engage the outer surface of the head plate I32.

Electrically conductive terminals I14, I16 extend through each of these plugs, these terminals being electrically connected to the conduits Ill] and I whichare connectedwith the signal lights as in the preceding embodiment. The ends:

movement of the corresponding pistons I36 and The operation .ofthis embodimentis substan-.

tially identical with that previously described, and further explanation. is believed ,to be unnecessary.

Since numerou modifications will readily occur to those skilled in the art, after a consideration of the foregoing specification and accompanying drawings, it is not desired to limit the invention to the exact construction shown and described, but all suitable modifications and equivalents may be resorted as falling within the scope of the appended claims.

Having described the invention, What is claimed as new is:

1. In a hydraulic brake system, a master cylinder and a slave cylinder assembly operatively connected thereto, individual wheel cylinders having hydraulic lines connected to said slave cylinder assembly, said slave cylinder assembly comprising a plurality of slave cylinders with pistons sliclable therein, an operative connection between said master cylinder and one end of said slave pistons, pressure chambers at the other end of each of said pistons, each of said pressure chambers being connected to one of said hydraulic lines, an intermittently operated electric switch in each of said pressure chambers for signaling a predetermined travel. of the piston therein, a second switch in each. chamber for indicating piston travel in excess of said, predetermined travel, fastening means for holding said second switch closed upon actuation thereof and a stop for limiting piston travel towards said switches, a signaling device and electric circuits connecting said switches thereto.

2. The combination of claim 1, including a plug mounted in each slave cylinder, and carryingeach of said switches and said stop. 3. The combination of claim 1, including a plug mounted in each slave cylinder, and carrying each of said switches and said stop, and said fastening means.

4. The combination of claim 1, wherein said slave cylinders are parallel and have a common closure plate for their pressure chambers, a plug extending through said plate and into each chamber, said switches being mounted in said plug and extending into said chambers-for actuating engagement by the respective pistons.

5. The combination. of claim 4, wherein said pair of switches have a common actuating member positioned in the path of movement of the piston for actuation thereby.

6. The combination of claim 5, wherein said fastener is mounted on said plug and is adapted to engage and retain said actuating member when the latter is moved into engagement with said REFERENCES CITED second switch.

7. The combination of claim 6, wherein said g erences are of record m the stop is carried by said plug.

8. The combination of claim 7, wherein said 5 UNITED STATES PATENTS actuating member is mounted on said stop. Number Name Date ELSWORTH MAPES' 1,557,330 Reynolds Oct. 13, 1925 RUSSELL 2,121,653 Davis Jan, 21, 1933 

